Method for integrated circuit fabrication

1. A method comprising: receiving a mask and a wafer, wherein the mask includes a plurality of units and each of the units corresponds to a first pattern of an IC and the wafer includes a substrate and a resist layer over the substrate; performing a first exposure to the resist layer using the mask; performing a second exposure to the resist layer using the mask, wherein a first image from the first exposure is superimposed with a second image from the second exposure, and the first and second images correspond to different ones of the units; repeating the performing of the second exposure until at least one image on the resist layer has been exposed to at least a full radiation dose; developing the resist layer; and etching the substrate using the developed resist layer as an etch mask.

2. The method of claim 1 , wherein the first and second exposures utilize an extreme ultraviolet (EUV) radiation.

3. The method of claim 1 , wherein a unit represents an image for a single die to be formed on the wafer.

4. The method of claim 1 , wherein the substrate includes silicon.

5. The method of claim 1 , wherein the plurality of units are arranged in an array with M columns and N rows, wherein the first exposure uses a first radiation dose less than a full radiation dose, and wherein the second exposure uses a second radiation dose less than the full radiation dose.

6. The method of claim 5 , wherein: the M is 3 and the N is 3; the first radiation dose is about one third of the full radiation dose; the second radiation dose is about one third of the full radiation dose; and two thirds of images from the second exposure are superimposed over two thirds of images from the first exposure.

7. The method of claim 5 , wherein the first radiation dose is about the same as the second radiation dose.

8. The method of claim 5 , wherein the mask is an EUV mask and the plurality of units includes at least one phase defect.

9. The method of claim 8 , wherein: the plurality of units includes a first unit and a second unit; the first unit includes a phase defect at a location of the first unit corresponding to a first location of the first pattern; the second unit is substantially free of phase defects at a location of the second unit corresponding to the first location of the first pattern; the first image corresponds to the first unit; and the second image corresponds to the second unit.

10. The method of claim 8 , wherein the at least one phase defect is one of: a bump defect and a pit defect.

11. A method comprising: receiving a mask, wherein the mask is patterned with a pattern of an IC to form a plurality of units including first and second units; receiving a wafer, wherein the wafer includes a substrate and a resist layer over the substrate; performing a first exposure to the resist layer using the mask with a first fractional radiation dose thereby forming a first plurality of images on the resist layer, wherein a first one of the images is exposed with the first unit; positioning the mask relative to the wafer such that a second exposure to the resist layer using the mask will superimpose an image of the second unit over the first one of the images; and performing the second exposure with a second fractional radiation dose.

12. The method of claim 11 , wherein the first and second fractional radiation doses are at least 1/N of a full radiation dose each wherein the N is the number of units on the mask.

13. The method of claim 11 , wherein the second fractional radiation dose is about the same as the first fractional radiation dose.

14. The method of claim 11 , further comprising: repeating the positioning of the mask and the performing of the second exposure until at least one of the first plurality of images has been exposed to at least a full radiation dose; developing the resist layer; and etching the substrate with the developed resist layer as an etch mask.

15. The method of claim 11 , wherein the substrate includes silicon.

16. The method of claim 11 , wherein the mask is a EUV mask having a phase defect.

17. A method comprising: receiving a mask, wherein the mask includes a plurality of die-layer images (dies) and each die is patterned with a first pattern of an IC; receiving a substrate and a resist layer over the substrate; performing a first exposure to the resist layer using the mask with a first radiation dose thereby forming a first plurality of images on the resist layer, wherein the first radiation dose is less than a full radiation dose; positioning the mask relative to the substrate such that a second exposure to the resist layer using the mask will superimpose at least one of the first plurality of images; performing the second exposure with a second radiation dose, wherein the second radiation dose is less than the full radiation dose; and repeating the positioning of the mask and the performing of the second exposure until at least one of the first plurality of images is exposed to at least the full radiation dose.

18. The method of claim 17 , further comprising: developing the resist layer; and etching the substrate with the developed resist layer as an etch mask.

19. The method of claim 17 , wherein: the plurality of dies includes a first die and a second die; the first die includes a phase defect at a location of the first die corresponding to a first location of the first pattern; the second die is substantially free of phase defects at a location of the second die corresponding to the first location of the first pattern; a first image of the first plurality of images is an image of the first die; a second image from the second exposure is an image of the second die; and the second image is superimposed over the first image by the second exposure.